: The overall goal of the study proposed here is to characterize RimJ and understand how RimJ controls transcription of the pyelonephritis-associated pili (pap) operon in response to changes in temperature. Expression of Pap facilitates attachment of uropathogenic Escherichia coli to epithelial cells and colonization of the upper urinary tract, leading to infections. Expression of the pap operon is controlled by temperature such that transcription occurs at 37 C, but not at lower temperatures (22-26 C). Mutations in rimJ lead to a loss of this thermoregulatory response such that transcription of the pap operon occurs at the nonpermissive temperature. RimJ is a N-terminal acetylase that modifies the ribosomal protein S5. In this study, the function of RimJ will be more fully characterized by obtaining additional mutations within rimJ. These mutants will be characterized for their effect on pap thermoregulation, RimJ stability, and acetylation activity. Along with the mutational study, DNA sequence analysis will be used to compare RimJ to other N-tenninal acetylases to determine areas of conservation that may delineate important functional domains of this enzyme. Two dimensional gel electrophoresis will be used to determine if S5 is the only substrate of RimJ or if it has another target that is important for pap thermoregulation. In addition, genetic techniques will be utilized to assess whether RimJ represses transcription in response to other environmental stimuli or if it controls other fimbrial operons besides pap, thus demonstrating whether RimJ is a more global regulator. These studies should provide illumination about the mechanism by which bacteria sense temperature and subsequently control gene expression. They will also shed light on the role of N-terminal acetylation, a process that is not well studied in prokaryotes. These studies are important clinically because there are several fimbrial operons that share regulatory mechanisms with pap that may also be controlled by RimJ. An understanding of how RimJ represses transcription is important as we look towards anti-infective strategies where signal transduction pathways can be targeted to prevent the expression of virulence determinants important for colonization.